The present invention is directed to apparatus and methods particularly suitable for precise aiming and delivery of magnetic stimulation, and more specifically, transcranial magnetic stimulation.
Transcranial magnetic stimulation (“TMS”) is a means of repetitively stimulating the human brain through an intact scalp and skull, i.e., non-invasively. TMS is delivered by passing a brief (200 microsecond), strong (10,000 volts, 6,000 amps) electrical current through a coil of wire (a TMS stimulator) placed adjacent to the head. The passage of electrical current induces a strong (2 Tesla) magnetic field which, in turn, induces electrical currents in nearby tissues. In the case of nerve cells, if the induced current is sufficiently intense and properly oriented, it will result in synchronized depolarization of a localized group of neurons (i.e., neuronal “firing”). Initially, magnetic stimulation was used only for peripheral nerves, in which instance it is affecting nerve fibers rather than neuronal cell bodies. More recently, magnetic stimulation has shown to be able to depolarize neurons in the brain. The cellular element of the brain being affected by TMS was assumed, but not proven, to be fibers rather than neuronal cell bodies.
TMS has several present and potential applications, in the domains of basic neuroscience research and of the treatment of brain disorders. Applications for neuroscience research include, for example: imaging brain connectivity; establishing inter-regional and inter-hemispheric conduction times; testing the function of specific brain areas by means of transient functional disruptions, so-called “virtual lesions”; and, studying the modification of synaptic efficacy induced by repetitive stimulation, termed LTP (long-term potentiation) and LTD (long-term depression). Potential clinical applications include, for example: pre-operative mapping, e.g., of language related brain areas; testing for neuronal conduction delays due to dysmyelinating disorders; and, treating brain disorders by selective modification (up or down regulation) of the synaptic efficacy of pathways (i.e., by inducing LTP and LTD).
Many TMS delivery systems are very crude. The TMS effector or stimulator (commonly referred to as a “TMS coil”) is a wire-wound coil, typically shaped like a “B.” The B-shaped coil is placed against the scalp and held in place by a human operator. For the primary motor cortex and primary visual cortex (small sections of the total brain surface), proper positioning is established by the elicited response: muscle contractions when stimulating the primary motor cortex; illusory lights (phosphenes) when stimulating the primary visual cortex. In both of these areas, the effects are very sensitive to coil position and orientation.
Structural and functional brain images can be used to fully specify TMS targeting by a robotic member, including the calculating and achieving optimal position and orientation of the coil relative to the scalp and brain surfaces. One method includes a method for optimally aligning a magnetic field relative to neuronal orientation, as inferred from the cortical surface orientation. Brain images are acquired prior to the TMS treatment session and used to compute an optimal pose (also termed the “treatment plan”) which is then robotically implemented in a second, subsequent TMS session.